Corona Treatment for Nanotransfer Molding Adhesion

Abstract

Corona discharge treatment offers a facile, robust, and scalable technique for adhesion promotion in nanotransfer molding. In contrast to conventional plasma treatment, which requires vacuum operation, corona treatment at ambient pressure enabled patterning of woodpile structures of PDMS with smaller feature dimensions (70 nm line width) and across a wider range of treatment doses. Similarities and differences between plasma (batch) and corona (continuous) treatment were established using dyne testing to capture the effects of treatment on surface wettability of PDMS. Evaluating spatiotemporal evolution of wettability through dyne tests enabled a common axis for direct comparison of the two process configurations in terms of dose. Both treatment types formed surface films of oxidized PDMS, which were characterized through compressive buckling tests of the PDMS–oxide bilayer. Corona treatment, by forming a thinner oxide film, extended the range of treatment doses and feature sizes exhibiting successful pattern transfer. Reduction in adhesion at high treatment dose was attributed to a weak boundary layer at the bonded interface. Demolding was studied via peel tests and AFM analysis to reveal that both plasma and corona treatment etch the stamp material (PFPE), underscoring the benefits of low treatment dose for process throughput as well as stamp lifetime. While both treatments displayed comparable etch rates as a function of dose, microscopic bumps on corona-etched stamps indicate a higher surface temperature compared to plasma-etched stamps. By optimizing adhesion for nanotransfer molding with a surface treatment well-suited to continuous processing, corona treatment provides a practical and economical approach to layer-by-layer additive manufacturing at the nanoscale.

Thin PDMS-on-Sacrificial-PCB Devices

“…As another useful function of the sacrificial-PCB device, the copper layer below the UV photoresist also constitutes a bottom electrode which enables pre-release PDMS electrical stimulations and characterizations. As shown in Figure a (schematic cross section), the PCB copper electrode underneath the thin UV photoresist can enable pre-release electrical stimulations such as electric fields for corona charging , or electrospinning on a thin insulating film. , Similarly, the PCB copper electrode allows us to perform pre-release impedance-based characterization of PDMS, which can simplify process development or provide an effective method for preliminary quality control. Importantly, impedance-based measurements may help to estimate the PDMS thickness (if the PDMS dielectric constant or conductivity is known) or its dielectric constant or conductivity (if the thickness is known), which are often crucial parameters.…”

Buckling Mechanics Modulus Measurement of Anisotropic Cellulose Nanocrystal Thin Films

“…The greater lateral resolution of the AFM was necessary to measure the small wavelengths of the wrinkled oxide layer. The thickness of the oxide layer was calculated by assuming the oxide modulus to be 70 GPa (that of SiO 2 ) on the basis of the previous work of Deagen et al and Bowden et al , The PDMS sample was compressively prestrained 5% and processed under the same corona treatment conditions as the CNC film samples. The compressive prestrain was released after corona treatment to induce a uniaxial compressive strain orthogonal to the prestrain direction on the surface of the PDMS, permanently wrinkling the corona-treated thin film.…”